Vitreous materials are generally manufactured from a mixture of raw materials, for example silicates, basalt, limestone, soda ash and other minor constituents which are introduced into a melter and melted into a viscous liquid state at temperatures in the order of 1250 to 1500° C.; the melt is then supplied to a forming process. Depending on the intended use of the melt, for example for manufacture of flat glass, hollow glass, continuous fibers, such as fibers for reinforcement purposes or fibers for insulation purposes, a melt refining step may be required upstream of the forming process. The chemical composition of the melt and its physical properties are selected as a function of the intended use and the forming process.
Vitrifiable material as referred to herein includes raw materials for glass melting or manufacturing, but also other raw materials, including but not limited to waste and recycled materials, that may be melted and vitrified, like stone, rock, shale, ceramics and the like. The present description mainly refers to glass melting, as an example, but obviously extends to the production of melts that may be different from glass in its narrow sense.
Conventional glass melters comprise an energy supply from above a glass melt surface, for example from burners generating a flame in a space between the glass melt surface and a crown of the melter, whereby heat is transferred to the glass melt by the flame itself and by radiation from the crown material. Raw batch material to be melted is loaded at the top of the glass melt in the melter and heat is transferred from the melt to the batch material which is incorporated into the melt.
In some glass melters, energy is supplied by electrically heated electrodes arranged below the surface of the melt; such electrodes may provide the only heat source or be used in combination with burners.
A further type of glass melter has one or more burner nozzles arranged below the surface of the melt such that the burner flames and/or combustion products pass through the melt. This arrangement is referred to as submerged combustion.
Such submerged combustion melters generate high volumes of exhaust fumes. In view of ever increasing requirements with respect to environmental pollution and/or sustainable production processes, it is required to transfer the exhaust gases through so-called afterburners. One of the major roles of an afterburner is to ensure complete combustion of potentially remaining combustible elements and reduction of NOx content in the exhaust fumes released to the environment. Generally such afterburners are mounted in the exhaust system and consist in an enlarged chamber allowing for increased residence time of given gas volumes in said enlarged chamber at conditions of temperature and pressure that are suitable for detoxification of the exhaust to a required extent. Depending on the arrangement of the exhaust system, the afterburner may require additional energy input, including heating and/or fuel injection, in order to generate the required pressure and temperature conditions for reaction of remaining combustible elements and/or detoxification of remaining reactive elements.